The relationship between physical activity during pregnancy and maternal and fetal disorders (e.g., preeclampsia, preterm birth, and low birth weight) is controversial. Conflicting findings are due, in large part, to the lack of instruments designed to assess physical activity during pregnancy. Current questionnaires misclassify activity patterns in pregnant women as the majority have been developed and validated in men, emphasize participation in moderate to vigorous sports, and fail to include household or childcare activity. No surveys account for the unique intensity of activity during pregnancy. This proposal will use an innovative approach to develop and validate the first pregnancy physical activity questionnaire (PPAQ). The study will be conducted among prenatal care patients at a large tertiary care facility in Western Massachusetts. Interviewer-administered physical activity recalls will be conducted among 150 patients (50 in each trimester) to establish the activities in which pregnant women engage. This is particularly important for a population whose activity habits have not previously been characterized. Activities that are important contributors to total energy expenditure, particularly to between person variance, will be selected for the PPAQ. In order to score the intensity of each activity, we will directly measure the metabolic cost of the activities via a portable metabolic measurement system among 30 patients (10 in each trimester). These findings will be integrated into a self- administered quantitative PPAQ. Finally, we will validate and calibrate the PPAQ among 60 patients (20 in each trimester) using a physical activity monitor, an objective measure of activity. Equipment and protocols available from preliminary studies will enable efficient and economical study conduct. The PPAQ will be the first validated instrument that can be used to determine the lower and upper levels of rigor (frequency, duration, intensity) for activity during pregnancy, and identify the specific parameters that characterize both threshold and dose response effects. This work will form the basis for investigations of physical activity and maternal and fetal disorders. Unlike many currently recognized risk factors for adverse pregnancy outcome, physical activity is potentially within the control of individual women.